1. Field of the Invention
The present invention relates to a tool and a tool holder to be used in a machine tool. More particularly, the present invention relates to a tool and tool holder removably attachable to the spindle of a machine tool.
2. Description of the Related Art
In a machine tool provided with a spindle such as machining center, the maximum rotational speed of the spindle is determined by the structure of a bearing rotatably supporting the spindle and a lubrication system of this bearing. For this reason, when it is necessary to rotate a tool at a higher rotational speed than the maximum rotational speed of the spindle, an accelerating apparatus is used.
As the accelerating apparatus, for example, an accelerating apparatus provided with a gear mechanism such as an epicyclic gearing which holds the tool and is removably attachable to the spindle is well known.
However, when raising the rotational speed of the tool to a higher speed than the maximum rotational speed of the spindle by the above gear mechanism, the accelerating apparatus increasingly generates heat at a super high rotational speed such as tens of thousands to hundreds of thousands of revolutions per minute, so the machining tolerance of a workpiece can be influenced by the heat. Further, at the above super high rotational speed, the noise from the accelerating apparatus can also increase. Furthermore, a highly reliable precision structure able to withstand the above super high rotational speed is required for the accelerating apparatus, so there is the disadvantage that the manufacturing cost becomes relatively high.